The present invention relates to a set of scales having at least one adjusting device provided with a drive.
In particular in precision scales or analytical scales, electric motors, usually configured as DC motors, are used for various adjusting functions.
In some cases, differently dimensioned motors are used for the different adjusting functions. Alternatively, for production or cost reasons, identical motors may be used, but then these motors are not optimally configured for their respective purposes.
DE 90 06 644 U1 discloses a set of scales with a wind shield which is moved by a motor. A wall element of a weighing chamber surrounding the scale pan is moved by an electric motor. A sensor serves to detect the position of the wall element.
In the case of known automatic weight switching for a set of scales, an adjusting weight lies on a weight support which can be lowered or raised through tilting about a tilt axis. Arranged parallel to the tilt axis is a rotation axis with an eccentrically mounted cam disk. A contact surface of the weight support, which is arranged at a right angle to the cam disk, is pressed by a spring against the cam disk. The rotation axis is driven by a DC motor via a gearbox. In order to fix the position of the eccentrically mounted cam disk or of the weight support, two disks with control cams are arranged on the rotation axis, whereby the control cams actuate switches assigned thereto in their respective predetermined end positions. Although this weight switching system has proved to be essentially effective in practice, the control cams with switches render the system relatively costly and also relatively bulky, due to the electric motor and the gearbox that are used.
A motor-driven weight switching and locking system is disclosed in, for example, DE 42 35 250 C1. A set of scales with a motor-driven movable contact surface is known, for example, from DE 198 28 515 A1. This set of scales using the principle of electromagnetic force compensation has a vertically movable load support, a position sensor, a variable gain amplifier and a coil in a magnetic field of a permanent magnet, as well as at least one contact surface which delimits the downward movement of the load support, at least one contact surface which delimits the upward movement of the load support and an electronic evaluation unit. At least one of the contact surfaces is movable. The movable contact surface is controlled with the aid of the position sensor such that the load support is held as far as possible in the same position as in normal weighing operation.
DE 28 41 996 C2 discloses a weight switching system for a beam balance, particularly for an analytical balance, comprising a plurality of cam shafts for lifting/lowering the weights and an electric motor drive that controls the cam shafts via sensors.
It is common to all the known sets of scales that the electric motors used are relatively bulky and require relatively complex gearboxes.
A further disadvantage is that due to the power dissipation that occurs from the electric motors, an undesirable level of heat can be generated. The electric motors can also produce undesirably large magnetic fields. The use of electric motors can also give rise to problems in explosion hazard areas.